The speed characteristics of the car of this type of conventional hydraulic elevator tend to change in principle when there is a variation in the load applied to the car and/or the temperature of the fluid and this causes a change in the flow controlled by means of the flow control valve or the flow intake by or flow discharge from a hydraulic pump. As a result, the terminal slowdown time is elongated, and this elongation deteriorates riding comfort, increases the energy loss and elongates the operation time, etc.
In order to overcome the above problems, an operating method for a hydraulic elevator has been proposed in, for example, U.S. Pat. No. 4,534,452 in which the actual start of the deceleration function is delayed to take place after the time at which a deceleration stopping/starting command is made when the terminal slowdown time is long. This operating method is carried out on the basis of an estimation of the actual speed of the car without the employment of any detector.
Namely, as described above, the flow of the pressurized fluid controlled through the flow control valve varies in accordance with the load applied to the car and changes in the fluid temperature. Such a variation is effected in accordance with a certain law.
A deceleration starting delay time is, therefore, calculated so as to obtain a desired terminal slowdown time by estimating the full speed, the terminal slowdown speed and the time required to bring down the speed from the full speed to the terminal slowdown speed. These factors are estimated in accordance with factors such as the load, the fluid pressure, and the fluid temperature of the hydraulic elevator which is operated.
However, in this conventional operating method the required factors to obtain the deceleration starting delay time are estimated by detecting the operating state of the hydraulic elevator. The accuracy and the convergence of the speed characteristics compensation, therefore, necessarily depend upon the estimated accuracy without exception.
As a result, it is difficult to estimate the value accurately because of the imprecise manufacture and the imprecise adjustment of the flow control valve. Accordingly, it is impossible to carry out a control for the hydraulic elevator with greater accuracy because of the deteriorations of the precisions during control and the convergence.